Nearly all disease states in multicellular organisms involve the action of proteins. Classic therapeutic approaches have focused on the interaction of proteins with other molecules in efforts to moderate the proteins' disease-causing or disease-potentiating activities. In newer therapeutic approaches, modulation of the production of proteins has been sought. A general object of some current therapeutic approaches is to interfere with or otherwise modulate gene expression.
One method for inhibiting the expression of specific genes involves the use of oligonucleotides, particularly oligonucleotides that are complementary to a specific target messenger RNA (mRNA) sequence. Due to promising research results in recent years, oligonucleotides and oligonucleotide analogs are now accepted as therapeutic agents holding great promise for therapeutic and diagnostic methods.
Oligonucleotides and their analogs can be designed to have particular properties. A number of chemical modifications have been introduced into oligomeric compounds to increase their usefulness as therapeutic agents. Such modifications include those designed to increase binding affinity to a target strand, to increase cell penetration, to stabilize against nucleases and other enzymes that degrade or interfere with the structure or activity of the oligonucleotide, to provide a mode of disruption (terminating event) once the oligonucleotide is bound to a target, and to improve the pharmacokinetic properties of the oligonucleotide.
One group of bicyclic nucleoside compounds having bicyclic sugar moieties that are conformationally locked is locked nucleic acids or LNA (Koshkin et al., Tetrahedron, 1998, 54, 3607-3630; U.S. Pat. Nos. 6,268,490 and 6,670,461). These compounds are also referred to in the literature as bicyclic nucleotide analogs (International Patent Application WO 98/39352), but this term is also applicable to a genus of compounds that includes other analogs in addition to LNAs. LNAs have been used in numerous studies where ribonucleoside mimics are desired. Such modified nucleosides mimic the 3′-endo sugar conformation of native ribonucleosides with the advantage of having enhanced binding affinity and increased resistance to nucleases. LNAs are discussed more thouroughly below.
One group has added an additional methlene group to the LNA 2′,4′-bridging group (e.g. 4′-CH2—CH2—O-2′ (ENA), Kaneko et al., U.S. Patent Application Publication No.: U.S. 2002/0147332, also see Japanese Patent Application HEI-11-33863, Feb. 12, 1999; U.S. Patent Application Publication Nos. 2003/0207841 and 2002/0147332).
Another publication reports a large genus of nucleosides having a variety of bicyclic sugar moieties with the various bridges creating a bicyclic sugar having a variety of configurations and chemical composition (U.S. Patent Application Publication No.: US 2002/0068708).
Despite these advances, a need exists in the art for the development of means to improve the binding affinity and nuclease resistance properties of oligomeric compounds.